Wide band aerial



1960 1 M. F. RADFORD 2,964,748

WIDE BAND AERIAL.

Nov. 12; Q 2 sheets-Sheet l INVENTOR 77 m 742M106 fcay BY a 7%? I ATTORNEYS Dec. 13, 1960 ML F. RADFORD WIDE BAND AERIAL 2 Sheets-Sheet 2 Filed Nov. 12, 1959 F/GZ.

A'rrcnnzYs United States Patent WIDEBAND AERIAL Matthew Frederick Radford, Danbury, England, assignor to Marconis Wireless Telegraph Company Limited This invention relates to wide band aerials and has for its object to provide improved wide band aerials suitable for use for ground-to-air communication and in other cases in which good radiation in all directions of azimuth and elevationi.e. gapless cover over substantially a hemisphereis required. So far as the present applicant is aware there is no known aerial which is capable of working over a wide band and which has no direction of azimuth or elevation in which the transmitted signal strength is zero or so low as to approximate to zero, highly desirable though it obviously is to provide such an aerial for such purposes as ground to air communication in which it may be necessary to communicate with an aircraft in any direction of azimuth or elevation from the ground station.

According to this invention an aerial comprises at least one feeder wound into a tapered coil the inter-turn pitch of which is varied progressively over the length thereof as a function of distance from the vertex of the taper and a plurality of radiator elements extending outwardly from the coil and arranged at quarter-turn intervals along it, each such element being of electrical length susbtantially equal to the electrical length of that quarter-turn which has its mid-point at the element in question.

According to a feature of this invention an aerial comprises at least one feeder wound into a tapered coil the inter-turn pitch of which decreases logarithmically from the base to the apex of the taper and a plurality of radiator elements extending radially outwards from the coil and arranged at quarter-turn intervals along it, the radiators being of logarithmically reducing lengths with the longer ones nearer the base and each such element being of electrical length substantially equal to the electrical length of that quarter-turn which has its mid-point at the element in question.

The radiator elements may be radial and each at right angles to the axis of the tapered coil but preferably they are radial but inclined upwardly to the (presumed horizontal) base of the tapered coil.

The coil is preferably circular in shape, i.e. it may lie on the surface of an imaginary right cone, but this is not essential and other shapes may be adopted, e.g. square with the coil lying on the surface of an imaginary right square pyramid.

Preferably the aerial is fed through an axially arranged feeder line connected to the vertex end of the tapered coil.

A member having an earthed conducting tapered surface inside and parallel to the imaginary surface on which the coil lies may be provided inside the coil. Where the feeder line is a co-axial cable this surface is preferably earthed to the outer conductor of the cable at the vertex end and also to the ground plane at the base end.

The bandwidth of an aerial in accordance with this invention is theoretically a function of the ratio of the length of the longest radiator element to the length of 2,964,748 Patented Dec. 13, 1960 2 the shortest radiator element and the longest useful wavelength is found to be approximately four times the electrical length of the longest radiator element.

In one embodiment which was successfully tested experimentally, the coil lay on the surface of an imaginary vertical right cone and the vertical distance between any two radiators one turn apart along the coil was made equal to the length of the shorter of the two radiators in question, the pitch of the coil decreasing logarithmically from the base to the apex of the cone and each element being of electrical length substantially equal to the electrical length of that quarter-turn which has its mid-point at the element in question. This embodiment was found to give unbroken cover over a hemisphere and to have a useful bandwidth of 340 to 700 mc./s., the polarisation being substantially circular at the zenith (the aerial was mounted with its axis vertical), substantially horizontal at the horizon and elliptical in intermediate horizontal planes. The vertical distance between any two radiators one tum apart along the coil is not critical and this vertical distance can be reduced to a value equal to half the length of the shorter of the two radiators in question without appreciable loss of performance. Varying this vertical spacing may be used to control the radiation pattern to some extent, increase in spacing tending to increase the horizontal power at the expense of the zenithal power.

The invention is not limited to the use of a single tapered coil as hereinbefore set forth. There may, for example, be two identical tapered coils intertwined at each with its own radiators. Any suitable conventional feeder system may be used for such a double coil aerial e.g. a central balanced line or balun or a co-axial cable inside or attached to one coil with its inner conductor connected to the other coil at the vertex.

The invention is illustrated in the accompanying drawings, which are simplified diagrammatic representations of two embodiments.

Referring to Fig. 1, the aerial therein shown is mounted with its axis vertical. It consists of a feeder 1 wound in the form of a tapered coil on an imaginary right cone with its base on the ground plane 2 and its vertex above the ground plane. The pitch of the helix is largest at the base and decreases logarithmically to a minimum value at the minimum diameter. Fixed and electrically connected to the coil are radially outwardly extending radiator elements 3, the elements being spaced along the coil at quarter-turn intervals so that there are four lots of elements lying in four mutually perpendicular vertical planes. The elements are inclined upwardly at a small angle as shown. The radiator elements decrease in length logarithmically from near the base of the cone towards the vertex, each element being of electrical length substantially equal to the electrical length of the quarter-turn at the middle of which it is attached. The spacing between any two radiator elements which are one turn apart along the coil is in the aerial actually shown, equal to the electrical length of the shorter of the two elements in question, but it may be of any value between this length and about half this length.

The aerial may be sup-ported mechanically in any convenient way, for example, by insulating support rods such as distrene rods 4. It is fed through a co-axial feeder 5 running along the axis of the aerial and having its inner conductor connected to the feeder 1 at the vertex and its outer conductor earthed.

In the modification shown in Figure 2 there are two tapered coils, each with its own radiators and each like the single tapered coil of the embodiment already described. The two coils are intertwined at 180 as shown, In Figure 2 the second coil and its radiators are given the same references as the first out with a tick suffix and the aerial is fed by a co-axial feeder CF a balun B and a balanced feeder BF the arrangement of which will be obvious from the drawing. 7

Although aerials in accordance with this invention have been herein described from the point of view of transmission, it will be obvious to those skilled in the art that they may equally be used for reception, providing, when so used, the same advantages of large bandwidth and unbroken cover over substantially a hemisphere.

I claim:

1. An aerial comprising at least one feeder wound into a tapered coil the inter-turn pitch of which is varied progressively over the length thereof as a function of distance from the vertex of the taper and a plurality of radiator elements extending outwardly from the coil and arranged at quarter-turn intervals along it, each such element being of electrical length substantially equal to the electrical length of that quarter-turn which has its mid-point at the element in question.

2. An aerial comprising at least one feeder wound into a tapered coil the inter-turn pitch of which decreases logarithmically from the base to the apex of the taper and a plurality of radiator elements extending radially outwards from the coil and arranged at quarter-turn intervals along it, the radiators being of logarithmically reducing lengths with the longer ones nearer the base and each such element being of electrical length substantially equal to the electrical length of that quarterturn which has its mid-point at the element in question.

3. An aerial as claimed in claim 1 wherein the radiator elements are radial and each at right angles to the axis of the tapered coil.

4. An aerial as claimed in claim 1 wherein the radiator elements are radial and each inclined outwardly away from the base of the tapered coil.

5. An aerial as claimed in claim 1 wherein the coil lies on the surface of an imaginary right cone.

6. An aerial as claimed in claim 1 and having an axially arranged feeder line connected to the vertex end of the tapered coil.

7. An aerial as claimed in claim 1 wherein the vertical distance between any two radiators one turn apart along the coil is between the length of the shorter of the two radiators in question and one half that length.

8. An aerial as claimed in claim 1 wherein there are two similar tapered coils intertwined at each with its own radiators.

9. An aerial as claimed in claim 1 wherein there is a member having an earthed conducting tapered surface inside and parallel to the imaginary surface on which the coil is situated.

No references cited. 

